I've been using the JournalPress plugin [ https://wordpress.org/plugins/journalpress/ ] with no difficulties. Do note that you will have to apply two tiny patches yourself; you can find the info on this in the support section for the plugin.

I tried using the LJ Crossposter plugin but preferred the way JournalPress handled things. I only installed Crossposter because it was supposed to add a link to the LJ crosspost to the Wordpress post, but either that function was broken, or I never enabled it properly.